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I. Schienbein

Publications and source records attributed to I. Schienbein.

At least 109 records · Page 6Linked to original sources
arXiv2005

Hadroproduction of D and B mesons in a massive VFNS

We present a calculation of the next-to-leading order cross section for the inclusive hadroproduction of D and B mesons as a function of the transverse momentum and the rapidity in a massive variable flavor number scheme. We compare our numerical results with recent data from the CDF Collaboration at the Fermilab Tevatron for the production of D^0, D^{*+}, D^+, and D_s^+ mesons at center-of-mass energy $\sqrt{S} = 1.96$ TeV and find reasonably good agreement with the measured cross sections.

hep-ph↗
arXiv2005

Collinear Subtractions in Hadroproduction of Heavy Quarks

We present a detailed discussion of the collinear subtraction terms needed to establish a massive variable-flavour-number scheme for the one-particle inclusive production of heavy quarks in hadronic collisions. The subtraction terms are computed by convoluting appropriate partonic cross sections with perturbative parton distribution and fragmentation functions relying on the method of mass factorization. We find (with one minor exception) complete agreement with the subtraction terms obtained in a previous publication by comparing the zero-mass limit of a fixed-order calculation with the genuine massles results in the MSbar scheme. This presentation will be useful for extending the massive variable-flavour-number scheme to other processes.

hep-ph↗
arXiv2004

Inclusive D^{*+-} Production in p p-bar Collisions with Massive Charm Quarks

We calculate the next-to-leading order cross section for the inclusive production of D^{*+-} mesons in p p-bar collisions as a function of the transverse momentum and the rapidity in two approaches using massive or massless charm quarks. For the inclusive cross section, we derive the massless limit from the massive theory. We find that this limit differs from the genuine massless version with MS-bar factorization by finite corrections. By adjusting subtraction terms, we establish a massive theory with MS-bar subtraction which approaches the massless theory with increasing transverse momentum. With these results and including the contributions due to the charm and anti-charm content of the proton and anti-proton, we calculate the inclusive D^{*+-} cross section in p p-bar collisions using realistic evolved non-perturbative fragmentation functions and compare with recent data from the CDF Collaboration at the Fermilab Tevatron at center-of-mass energy root(S) = 1.96 TeV. We find reasonable, though not perfect, agreement with the measured cross sections.

hep-ph↗
arXiv2004

Pion Rescattering in Nuclei

Nuclear corrections are presented for neutrino and electron induced reactions in a pedagogical manner. The formalism is demonstrated with numerical studies and is shown to produce substantial corrections in channels where the pions have the same charge with the exchanged current. Two comparisons with available data show consistency of the model. Further studies along these lines will improve the accuracy of the results and enhance the discovery potential of experiments.

hep-ph↗
arXiv2004

Comparison of a new Delta resonance production model with electron and neutrino data

We consider resonance production by neutrinos focusing on the dominant resonance $P_{33}$ at low energies with a detailed discussion of its form factors. The results are presented for free nucleon targets. The $Δ$ resonance is described by two form factors $C_3^V$ and $C_5^A$ and its differential cross sections are compared with experimental data. Further, we apply this approach to the electroproduction case and calculate its differential cross sections which are compared with electroproduction experimental data. Our approach to the analysis of $Δ$ resonance is particularly simple and self-contained such that it could be helpful for the physical interpretation.

hep-ph↗
arXiv2004

Inclusive $D^*$ hadroproduction with massive quarks

A calculation of the next-to-leading order cross section for the inclusive hadroproduction of charm quarks including heavy quark mass effects in the hard scattering cross sections is presented. It is described how the massive hard scattering cross sections are constructed from the corresponding cross sections in a fixed order calculation where collinear pieces associated with the heavy quark are not yet subtracted. By adjusting suitable subtraction terms a massive theory with MSbar subtraction is established which approaches the massless theory with increasing transverse momentum. These results will allow to have a more solid comparison with recent data for the inclusive $D^{\star\pm}$ cross section in $p\pbar$ collisions from the CDF collaboration at the Tevatron at $\sqrt{S} = 1.96 \tev$.

hep-ph↗
arXiv2003

CP violation in polarized $b \to d l^+ l^-$: A Detailed Standard Model Analysis

The electroweak CP violating rate asymmetries in the decay $b \to d l^+ l^-$ are reexamined in detail and updated. In particular, the rate asymmetries are studied when one of the final state leptons is polarised. We find an estimate for the asymmetry of (5-15)% in the polarised decay spectrum which is close to known results for the unpolarised case. Interestingly, in the region separating the $ρ-ω$ and $c \bar c$ resonances, which is also theoretically cleanest, the polarised contribution to the asymmetry is larger than the unpolarised result. A $3σ$ signal for direct CP violation, requires about 10^{10} $B \bar B$ pairs at a B factory. In general these results indicate an asymmetric contribution from the individual polarisation states to the unpolarised CP asymmetry; an atribute for any new physics searches.

hep-ph↗
arXiv2003

Muon spectra of Quasi-Elastic and 1-pion production events at the KEK LBL neutrino oscillation experiment

We present predictions for the flux averaged muon energy spectra of quasi-elastic (QE) and 1-pion production events for the K2K long-baseline experiment. Using the general kinematical considerations we show that the muon energy spectra closely follow the neutrino energy spectrum with downward shift of the energy scale by 0.15 GeV (QE) and 0.4 GeV (1-pion production). These predictions seem to agree with the observed muon energy spectra in the K2K nearby detector. We also show the spectral distortion of these muon energy spectra due to the neutrino oscillation for the SK detector. Comparison of the predicted spectral distortions with the observed muon spectra of the 1-Ring and 2-Ring muon events in the SK detector will help to determine the oscillation parameters. The results will be applicable to other LBL experiments as well.

hep-ph↗
arXiv2003

Muon Spectra of Quasi-Elastic and 1-Pion Production Events in LBL Neutrino Oscillation Experiments

The muon energy spectra of the quasi-elastic and 1-pion production events in a LBL experiment, like K2K, are predicted to follow closely the neutrino energy spectrum, with downward shifts of the energy scale by $ /2 M$ and $( + M_Δ^2 - M^2)/2 M$ respectively. These predictions seem to agree with the observed muon spectra in the K2K nearby detector. The corresponding muon spectra in the far-away (SK) detector are predicted to show characteristic spectral distortions induced by $ν_μ$ oscillation. Comparison of the predicted spectral distortions with the observed muon spectra of the 1-Ring and 2-Ring muon events in the SK detector will help to determine the oscillation parameters. The results will be applicable to other LBL experiments as well.

hep-ph↗
arXiv2003

Pion absorption and rescattering in the ANP model revisited

Single pion leptoproduction in the region of the (3,3) resonance is currently of high interest for at least two reasons: (i) These reactions constitute an important part of the total cross section in low energy reactions and are utilized to detect neutrino oscillations in current and future long baseline experiments. (ii) Intranuclear rescattering of the pions in heavy nuclei results in interesting and sizable modifications of the free nucleon cross sections which are testable in electroproduction experiments. In this article we give a basic introduction to the pion multiple scattering model of Adler, Nussinov, and Paschos (ANP) with special emphasis on pion absorption. We also estimate the probability of multiple scattering.

hep-ph↗
arXiv2003

Standard Model CP violation in Polarised b->d l^+ l^-

In the standard model, we study CP violating rate asymmetries in the decay b->d l^+ l^- when one of the leptons is polarised. We find an asymmetry of (5 -- 15)% in the polarised decay spectrum which is comparable to known results for the unpolarised case. In the kinematic region separating the rho-omega and $c \bar c$ resonances, which is also theoretically cleanest, the polarised contribution to the asymmetry is larger than the unpolarised results. In order to observe a 3 sigma signal for direct CP violation in the polarised spectrum, assuming 100% efficiency, about 10^10 $B \bar B$ pairs are required at a B factory. Our results indicate an asymmetric contribution from the individual polarisation states to the unpolarised CP asymmetry. Taking advantage of this, one can attribute any new physics to be most sensitive to a specific polarisation state.

hep-ph↗
arXiv2002

Delineating the polarized and unpolarized photon distributions of the nucleon in eN collisions

The production rates of lepton-photon and dimuon pairs at the HERA collider and the HERMES experiment are evaluated in the leading order equivalent photon approximation. It is shown that the production rates are sufficient to facilitate the extraction of the polarized and unpolarized equivalent photon distributions of the proton and neutron in the available kinematical regions. It is pointed out that these results indicate the possibility of additional, independent, tests concerning the unpolarized and polarized structure functions F_{1,2}^N and g_{1,2}^N, respectively, of the nucleon.

hep-ph↗
arXiv2002

Two-Photon Processes and Photon Structure

In this article aspects of photon-photon physics related to the structure of real and virtual photons are reviewed. A re-calculation of the virtual photon-photon box is performed and some discrepancies in the literature are clarified. A useful compilation of various relevant limits derived from the most general expressions is provided. Furthermore, structure functions of spin-averaged, transverse and longitudinal virtual target photons are defined and discussed. Finally, the factorization of two-photon processes in the Bjorken limit is demonstrated to hold also for the case of virtual target photons.

hep-ph↗
arXiv2001

Heavy Quark Production in CC and NC DIS and The Structure of Real and Virtual Photons in NLO QCD

This thesis consists of two parts. In the first part heavy quark production in neutral current and charged current DIS is studied within the variable flavor number scheme of Aivazis, Collins, Olness, and Tung (ACOT). For this purpose all the relevant partonic subprocesses have been calculated to order O(α_s^1) for general masses and couplings taking into account massive initial state quark-partons as needed in the variable flavor number scheme of ACOT. By the calculation of the before missing radiative corrections to scattering amplitudes on massive quark partons the ACOT scheme could be completed to full order O(α_s^1). These results might also prove useful for studying the intrinsic charm content of nucleons. In the second part the parton content of pions and real and virtual photons is analyzed in leading order (LO) and next-to-leading oder (NLO) QCD within the framework of the radiative parton model of Glück, Reya, and Vogt (GRV). Furthermore, the factorization of the cross section for the process e^+ e^- -> e^+ e^- X into fluxes of transverse/longitudinal target photons and the cross sections for deep inelastic scattering off these target photons is investigated in detail. It is demonstrated that the factorization remains valid also for virtual P^2 \= 0 target photons in the Bjorken limit P^2 << Q^2. However, the neglected terms are of the order O(\sqrt{P^2/Q^2}) only and not of the order O(P^2/Q^2) as might have been naively expected. Finally, the photon structure functions have been calculated in lowest order perturbation theory according to the doubly virtual box γ^*(P^2) γ^*(Q^2) -> q \bar{q}. A useful compilation of various limits of these general expressions is provided.

hep-ph↗
arXiv2001

The Photon Structure Function at Small-x

It is shown that recent small-x measurements of the photon structure function F_2^γ(x,Q^2) by the LEP-OPAL collaboration are consistent with parameter-free QCD predictions at all presently accessible values of Q^2.

hep-ph↗
arXiv2000

Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?

It is demonstrated that present $e^+e^-$ and DIS ep data on the structure of the virtual photon can be understood entirely in terms of the standard `naive' quark--parton model box approach. Thus the QCD renormalization group (RG) improved parton distributions of virtual photons, in particular their gluonic component, have not yet been observed. The appropriate kinematical regions for their future observation are pointed out as well as suitable measurements which may demonstrate their relevance.

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